Various methods exist for the evaluation of combustion processes.
A plurality of motoric characteristic variables and conditions can be detected on the basis of combustion chamber pressure transducers. Motoric characteristic variables and conditions include, for example, actual load, misfires, combustion position, et cetera. This method requires an additional bore per cylinder in the cylinder head as well as a transducer which is adequate for series manufacture. These disadvantages as well as the high system costs presently hinder a use in series production.
The rough-running method is presently used for the detection of combustion misfires. For high-cylinder engines, the disturbance spacing is problematic with small loads.
In order to determine individual combustion-related parameters and conditions, it has overall been shown that a plurality of additional sensors and methods are applied when there is no combustion chamber pressure signal.
From the literature, it is known that the pressure information is transferred into the structure-borne noise in a complicated manner. No methods are known which make possible a complete reconstruction of the pressure signal from the structure-borne noise under practice-relevant conditions.
In U.S. Pat. 5,119,783, a method and an arrangement for determining the trace of the internal pressure of a cylinder of a piston engine is introduced. Here, a transfer function of the structure-borne noise is identified in the cylinder internal pressure. Thereafter, the computation of the cylinder of the cylinder pressure takes place by applying the previously identified transfer function to the measured structure-borne noise signal. Utilizing gate signals, only signal sections of the presure signal is reconstructed. The evaluation of the internal pressure trace over the entire work cycle is not provided. The transfer function is not dependent upon time or crankshaft angle within the signal window pregiven by the gate circuit.
In DE 196 12 180 C1, a method for detecting irregular combustion noises on a multi-cylinder diesel engine is introduced. Here, the combustion noise is used for feature extraction by means of structure-borne noise transducers. It can be assumed that even higher frequency signal components are applied. This method cannot be applied to spark-ignition engines since the higher frequency signals, which are generated in the structure-borne noise by normal combustions, can hardly be distinguished from disturbance noises.
In U.S. Pat. 5,005,549, a method for determining defective combustions is derived from the known principle of knock detection from structure-borne noise. For this purpose, the structure-borne noise signal is evaluated in an additional measurement window between the ignition time point and the actual knock window at idle. No information is obtained as to the frequency range which permits the detection of defective combustions.
An open-loop control and a closed-loop control of the combustion in the combustion chamber of an internal combustion engine is known from U.S. patent application Ser. No. 09/508,070, filed on Aug. 24, 1998. This open-loop control and closed-loop control is based on the reconstruction of the combustion pressure trace from signals of the knock sensors.
In U.S. Pat. 5,400,648, a method and an arrangement for determining the trace of the internal pressure of a cylinder of a piston engine is introduced. Here, a transfer function of the structure-borne noise is identified in the cylinder internal pressure. Thereafter, the computation of the cylinder pressure takes place by applying the previously identified transfer function to the measured structure-borne noise signal. Utilizing gate signals, only signal sections of the pressure signal are reconstructed. The evaluation of the internal pressure trace over the entire work cycle is not provided. The transfer function is not dependent upon time or crankshaft angle within the signal window pregiven by the gate circuit.
The limitation to specific signal segments is justified with the suppression of noise components in U.S. Pat. 5,400,648. However, this limitation leads beyond this suppression to the loss of useful data. The pressure signals of all cylinders are imaged in a crankshaft angular range of 720xc2x0KW in four-stroke engines. For this reason, an increasing overlapping of the pressure signals of different cylinders takes place with an increasing number of cylinders. The signal windows become correspondingly narrower in which the signal of a cylinder remains uninfluenced from the in-coupling of other cylinders.
The application of this method for detecting all features extractable from the cylinder internal pressure is therefore not possible for multi-cylinder engines.
The object of the invention is the development of a method and an arrangement wherein only the combustion-relevant parameters and conditions are extracted from the structure-borne noise signal.
Examples of combustion-relevant parameters are the integral of the combustion increase in the pressure signal, the integral of the pressure signal in the increase phase before reaching the maximum and the position of the maximum of the pressure signal. The pressure signal includes a component which is only attributable to the compression. This component could be measured, for example, without ignition. The pressure correlates with the volume above the piston and is therefore low with a large volume in advance of the compression stroke and at the end of the work cycle and is maximal in the region of the smallest volume at top dead center at the end of the compression stroke.
The combustion increase is the difference between the pressure traces which occur with and without combustion. The integral of the combustion increase is a measure for the energy conversion of the combustion. This measure is especially informative for the detection of the combustion misfires. The pressure integral of the buildup phase is suitable for load detection, that is, for detecting the cylinder charge. The position of the maximum is especially interesting for control purposes.
The solution of the task in accordance with the invention comprises that a model becomes effective for the method of the invention and the arrangement of the invention. This model also takes a time or crankshaft angle dependent transfer between pressure and structure-borne noise as a basis also for the relevant low frequency oscillations such as the changing pressure curves and the increases caused by combustion. The time dependency is realized by an angular-dependent transfer function in order to obtain an independency of engine speed.
The invention is based upon the realization that there exists a time dependent and/or crankshaft angle dependent transfer function(s) for the transfer between pressure and structure-borne noise signals. This dependency is explainable to a limited extent by the piston movement during the occurrence of the knock oscillations. The pressure oscillations generated by the knocking, in turn, undergo a frequency modulation because of the movement of the piston.
Only individual components of the reconstructable pressure signal are used for the determination of the combustion-relevant parameters and conditions. For the misfire detection, the reconstruction of the combustion increases in the order range is applied. Here, the term xe2x80x9corderxe2x80x9d identifies whole number multiples of the ignition frequencies. The ignition frequency of a cylinder of a four-stroke engine lies at half the crankshaft rotational frequency n/2, that is, at the camshaft frequency. For z cylinders, the frequency of the ignitions of the engine correspondingly lies at z*n/2.
The dc component of the combustion increase is represented by the zero Fourier coefficient, for example, for a Fourier transformation of the pressure signal out of the time domain into the frequency domain.